Coryneform bacteria are industrial microorganisms that have been widely used to produce amino acids and various nucleic acids. Coryneform bacteria are gram-positive bacteria that are used to produce chemical substances having various industrial applications in the areas of animal feed, drugs, food processing, or the like, which include amino acids such as L-lysine, L-threonine, L-arginine, and glutamic acid, and various nucleic acids, and require biotin for growth. They are characterized by snapping division, and having little tendency to degrade produced metabolites. Such coryneform bacteria are exemplified by the genus Corynebacterium including Corynebacterium glutamicum, the genus Brevibacterium including Brevibacterium flavum, Arthrobacter sp., and Microbacterium sp.
As one of L-amino acids, L-lysine is commercially used as an animal feed supplement, because of its ability to improve the quality of feed by increasing the absorption of other amino acids, in human medicine, particularly as ingredients of infusion solutions, and in the pharmaceutical industry. Therefore, the industrial production of lysine has become an economically important industrial process.
To improve the lysine production efficiency, the enzymatic activity of the biosynthetic pathway has been increased by amplifying individual genes in the lysine biosynthetic pathway or modifying their promoters. Corynebacterium strains anchoring enhanced genes involved in lysine biosynthesis and methods of producing L-lysine are well known in the art. For example, U.S. Pat. No. 6,746,855 discloses corynebacteria strains with an enhanced lysE gene (lysine export carrier gene), to which genes selected from the group consisting of a dap A gene, a lysC gene, a pyc gene and a dapB gene are additionally introduced, and a method for the production of L-lysine by cultivating the strains. In addition, U.S. Pat. No. 6,221,636 discloses a coryneform bacterium carrying a recombinant DNA comprising a DNA sequence coding for aspartokinase, in which the feedback inhibitory activity of L-lysine and L-threonine is substantially desensitized, and a DNA sequence coding for a diaminopimelate decarboxylase. US Pat. Application No. 20060003424 discloses a method of producing L-amino acid using coryneform bacteria which has an improved enzymatic activity by modification of the promoter for GDH gene, CS gene, ICDH gene, pDH gene, or ACO-producing gene to make it close to a consensus sequence.
To develop high titer strains from such coryneform bacteria by genetic engineering or metabolic engineering, the expression of genes involved in several metabolic pathways should be selectively regulated in coryneform bacteria. To this end, it is important to regulate the activity of a promoter, which is a regulatory region and recruits RNA polymerase to initiate transcription of DNA molecule.
Until now, there is no report of coryneform bacteria which has a high expression rate by improvement of the promoter of aspartate aminotransferase (EC; 2.6.1.1; aspB) gene which is considered to play an important role in the supply of a lysine precursor, aspartate in the lysine biosynthetic pathway.